1. Field of the Invention
This invention relates to a variable valve apparatus of an internal combustion engine which can change the drive phases and valve lift amounts of an intake valve and an exhaust valve.
2. Description of the Related Art
Knowledge is widespread about technologies for changing the phases and lift amounts of valves of an intake and exhaust system in accordance with the operating status of an internal combustion engine, for example, an automobile engine for the purposes of dealing with emission gases and reducing fuel consumption. A vane type variable phase valve apparatus for continuously changing a cam phase by a hydraulic force is known as a variable valve apparatus used in these technologies.
Knowledge is also abundant of a cam-switched valve apparatus which switches among a plurality of cams in accordance with the operating status of an internal combustion engine to adapt the drive phases and lift amounts of valves to the operating status.
Knowledge is also ample about a mechanical continuous variable valve apparatus which can be arranged to change the drive phases and lift amounts of valves by use of gears driven by stepping motors, intermediate levers and return springs (see, for example, Japanese Patent No. 3245492).
A vane type variable phase valve apparatus can shift the drive phase of a valve by changing the position of a vane, but cannot change the lift amount of the valve.
A cam-switched valve apparatus or a mechanical continuous variable valve apparatus, on the other hand, can shift the lift amount and phase of a valve. However, the cam-switched valve apparatus requires a plurality of cams, thus using many components and involving a complicated structure. The mechanical continuous variable valve apparatus needs, separately, a mechanism for changing the lift amount and a mechanism for shifting the phase, thus resulting in a complicated structure and large dimensions.
With a conventional ordinary continuous phase variable valve apparatus, when the valve closing timing of the intake valve is retarded, the valve opening start timing is also retarded. Thus, a valve overlap of the intake valve and the exhaust valve is decreased or lost, thereby posing the problem that poor fuel economy due to a pumping loss occurs.
In addition, these variable valve apparatuses often have a large height on account of their structure. Since the variable valve apparatus is installed above the cylinder head of an engine, the height of the entire engine is often great. Because of its complicated structure, moreover, a high accuracy of position is required of components to be operated in interlocked relationship. Their designing is so difficult that setting of desired valve lift characteristics has not been easy.